1. Field of the Invention
This invention relates to an industrial truck, such as a fork-lift truck, with an electrical drive system and an energy supply based on gaseous media.
2. Technical Considerations
An internal combustion engine is the preferred power source in industrial trucks that are required to have relatively high load-carrying capacities and performance requirements. Diesel engines are in very widespread use in these applications because they can be operated very economically and the fuel supply system is simple. However, diesel engines cannot be used if the truck is frequently operated indoors, such as in closed factory buildings, for example.
Battery-operated industrial trucks need very large battery capacities and, therefore, require long charging times to achieve the required high performance. To reduce down times, discharged batteries can be removed completely and replaced with charged batteries. For this purpose, the batteries are generally located in a tray-shaped device which, on counterweighted fork-lift trucks, is located between the axles underneath the driver's seat. However, the replacement of this battery tray is a very complex operation and the maintenance of a supply of replacement batteries is expensive.
An alternative to battery operation is offered by gas-powered fork-lift trucks. On these trucks, an internal combustion engine is operated with a mixture of gases, generally propane and butane or natural gas, which can be stored in appropriate pressure vessels. Some gases and mixtures of gases, such as mixtures of propane and butane for example, can be in liquid form at room temperature if under sufficiently high pressure. For purposes of the following discussion, these liquefied gases are also to be considered a “gaseous medium”. The emissions levels for this type of gas propulsion system are significantly lower than for diesel engines, while costs and down times are significantly less than with battery operation because the fuel tanks are generally located so that empty tanks can easily be replaced with full tanks. In addition, the costs of purchasing and maintaining these trucks are lower than for an industrial truck that has an electrical propulsion system and its related batteries and recharging units.
Fuel cell technology offers an alternative to both gas-powered operation and battery operation. Here too, an energy source that is in the form of a gas at room temperature is used, generally hydrogen, along with one which can be stored in liquid form in a thermally insulated pressure vessel. Hydrogen as an energy source can also be used as fuel in an internal combustion engine to which modifications have been made. The hydrogen tank is installed in a manner similar to that used for the attachment of a gas tank. For example, on a counterweighted fork-lift truck, the hydrogen tank is installed on the counterweight. The advantage of a fuel cell system is primarily the total absence of harmful emissions and simultaneously its very high efficiency. Therefore, it is frequently desirable to convert industrial trucks that have an electrical propulsion system so that they can use this energy source. However, the cost of this conversion is significant on account of the gas supply system that must be installed.
Gas tanks for gases under pressure are generally installed in the upper outside area of the industrial truck, for example on counterweighted fork-lift trucks on the counterweight, because they must be easily replaceable and, therefore, readily accessible. However, in that area, they frequently interfere with the operator's field of vision, in particular when the industrial truck is being operated in reverse, and may not be sufficiently protected against damage. With this layout, moreover, the two essential components of the energy supply, namely the energy storage mechanism and the energy converter, are located separately from each other, which requires long lines or conduits that are complex and are expensive to install.
Therefore, it is an object of the invention to provide an industrial truck, such as a fork-lift truck, that has an electrical drive system and an energy supply based on at least one gaseous medium, which has an unrestricted field of view for the driver on all sides, a secure installation of easily replaceable pressurized fuel tanks, and a compact layout of the components used to generate the electrical energy.